For most of the English political class the Scottish question was solved with the devolution settlement at the end of the 20th century. But that settlement is starting to look increasingly unstable. The Scottish parliament raised expectations that it has been unable to satisfy - and as the idea of abolishing it again is unthinkable the only possible move may be towards deeper devolution or full independence. A recent opinion poll found 51% of Scots supporting full independence.

Michael Fry, the rightwing Scottish historian, has now opened a new front in the independence debate by presenting a conservative case for breaking up Britain. Writing in the new issue of Prospect magazine, the former Scottish Conservative says that the real Scotland of staunch individualists and conservative Calvinists has been smothered by a politically correct public sector culture designed to keep the Scots cosseted and dependent. The only way to shake off this culture, which among other things is strangling the Scottish economy, is to move to full independence. The anomaly of a Conservative party that is anti-nationalist (at least in Scotland) and a Nationalist party that is to the left of the main centre-left party must end - and, he says, there are voices within the SNP now speaking out against the party's leftward drift.

Some of Fry's account does not sound plausible. Surely it is the Scottish centre-left which is disproportionately influential in both Scotland and England. And it is surely English grievance at Scottish political over-representation and its higher share of public spending which is more solidly based. Moreover, the idea that a statist social democracy is an external imposition from England will come as a surprise to generations of Scottish socialists. On the other hand there is something to the idea that Scottish independence has been sacrificed for the greater good of the British centre-left. It is widely assumed on the British left that the English would never on their own elect Labour governments to Westminster (despite the fact that Labour won a majority of English seats in each of the last three elections). So Britain needs left majorities in Scotland and Wales as a counter-weight to the neo-Thatcherite English majority, and to help keep the forces of nationalism at bay that has required political and economic sweetners, especially for Scotland.

Fry is also surely correct in his implicit assumption that Scottish Conservatism remains dead and he may well be right that embracing Scottish nationalism is the best way of reviving it. If Fry succeeds in converting many other Tories into SNP voters that will make it even more likely that the party will form the biggest party in the Scottish parliament after next May's election (just after the 300th anniversary of the union). The Scottish Lib Dems will reject a referendum on independence as a condition of joining a coalition. But what if the SNP are still the biggest party at the following election four years later? A referendum then might become inevitable, and there would be many more English voices cheering Scotland to the exit door than there would have been 15 years ago.

This is all another potential headache for Gordon Brown. But if something like it does start to happen the Scots and the English are going to have to think hard about what is the point of the British union. The recent success of the Irish model suggests to many Scots that independence earlier in the 20th century would have led to much greater prosperity and self-confidence. And would the losses to England from the end of the union be compensated for by having a less resentful neighbour to its north?